Acrylonitrile polymer composition stabilized with formaldehyde, a phenol, and an inorganic acid and method of making same



United States Patent ACRYLONITRILE POLYMER COMPOSITION STA- BILIZED WITHFORMALDEHYDE, A PHENOL, AND AN INORGANIC ACID AND METHOD OF MAKING SAMERichard R. Holmes, Bethesda, Md., and Lloyd T. Jenkins,

Decatur, Ala., assignors to The Chemstrand Corporation, Decatur, Ala., acorporation of Delaware N0 Drawing. Application May 23, 1956 Serial No.586,667

20 Claims. (Cl. 26032.6)

This invention relates to the stabilization of acrylonitrile polymersand blends thereof. More particularly, it relates to the stabilizationof acrylonitrile polymers and blends thereof which have a tendency todevelop color upon standing or application of heat.

The term polymer, as employed in the instant description and claims, isintended to include homopolymers, copolymers, and blends thereof, saidpolymers, containing at least 80 percent by weight of polymerized orcopolymerized acrylonitrile in the polymer molecule.

Acrylonitrile polymers containing 80 percent or more of acrylonitrileare generally insoluble in the more common solvents. In those instanceswhere suitable solvents have been found, in order to effect solution,the application of heat is usually necessary. Where heat is employed toeffect solutions, from which shaped articles are to be formed, a tan todark brown color frequently develops in the solutions and therefore iscarried over into the product formed therefrom. This color also developsin solutions upon standing for prolonged periods of time.

The mechanism which causes color formation has not been definitelyascertained, although a variety of reasons therefor have been advanced.The presence of metal ions, such as iron, copper and manganese in thesolutions may cause the color. The employment of amide compounds assolvents may result in formation of amines when heat is applied andcause color in the compositions. Impurities present in the solvents havealso been cited as a cause. Whatever may be the reason for colorformation, it results in compositions and products of undesirablestandards and therefore, has been the source of concern, particularly incommercial operations where such types of polymers or copolymers areemployed.

Accordingly, it is an object of the present invention to preventundesirable color formation in acrylonitrile polymer compositions.

Another object is to minimize color formation when solutions of theacrylonitrile polymers are permitted to stand for a prolonged period oftime or upon application of heat.

It is also an object of the invention to prevent color formation inacrylonitrile polymers at elevated temperatures.

A still further object of the invention is the production of solutionsof acrylonitrile polymers and articles produced therefrom havingimproved color characteristics.

Other objects and advantages will be apparent from a consideration ofthe description of the invention which follows hereafter.

In general, the objects of the invention are accomplished by dissolvingthe polymer of acrylonitrile in a suitable solvent therefor andpreventing or minimizing color formation by the presence in the solutionas an inhibiting agent, a combined reagent comprising formaldehyde, acompound having the general formula,

wherein R is hydrogen, methoxy, ethoxy or an OH group; and an inorganicacid having an ionization constant greater than 1 X 10".

The components of the inhibiting agent may be employed in equal orunequal amounts, any one consituent being present in a range of from 98tol percent in a three component system. The total amount of inhibitingagent may be employed in a range of about 0.3 to 15 percent, based onthe total polymer weight. However, it is preferred that the inhibitingagent of the instant invention be present in a small amount compared tothe amount of polymer dissolved. Thus, although the amount is notcritical, it is preferred that the inhibiting agent be present in theamount of about 0.3 to 3 percent, based on the total weight of thepolymer. The inhibiting agent may be added to the solvents before orafter the polymer is dissolved therein. The inhibiting agent permitsexposure to high temperatures for prolonged standing periods without thedevelopment of the objectionable color which usually results in suchsolutions. The compositions of the instant invention may be prepared ina varying temperature range. For example, the compositions of theinstant invention may be prepared by mixing the polymer, a suitablesolvent and the inhibiting agent at any temperature or heating themixture to a temperature up to the boiling point of the solvent.

Among the compounds bearing the general formula,

which may be employed in practicing the instant invention are phenol,p-methoxy phenol, p-ethoxy phenol, hydroquinone, etc.

Among the acids which may be employed in practising the instantinvention are sulfuric acid, nitric acid, phosphoric acid, hydrochloricacid, etc.

Among the solvents which may be used in practising the instant inventionare N,N-dimethylforrnamide, N,N- dimethylacetamide, aqueous zincchloride, sulfuric acid, aqueous nitric acid, aqueous sodiumthiocyanate, ethylene carbonate, sulfolane, nitromethane, etc.

The polymeric materials, which may be employed in the practice of thepresent invention, are polyacrylonitrile, copolymers, including binaryand ternary polymers containing at least percent by weight ofacrylonitrile in the polymer molecule, or a blend comprisingpolyacrylonitrile or copolymers comprising acrylonitrile with from 2 to50 percent of another polymeric material, the blend having an overallpolymerized acrylonitrile content of at least 80 percent by weight.While the preferred polymers employed in the instant invention are thosecontaining at least 80 percent of acrylonitrile, generally recognized asthe fiber-forming acrylonitrile polymers, it will be under-stood thatthe invention is likewise applicable to polymers containing less than 80percent acrylonitrile and the same stability is realized with theinhibiting agents defined herein. The acrylonitrile polymers containingless than 80 percent acrylonitrile are useful in forming films, coatingcompositions, molding operations, lacquers, etc., in all of whichapplications the alleviation of undesirable color is extremelyimportant.

For example, the polymer may be copolymer of from 80 to 98 percentacrylonitrile and from 2 to 20 percent of another monomer containing theC=C linkage and copolymerizable with acrylonitrile. Suitablemonoclofinic monomers include acrylic, alphachloroacrylic andmethacrylic acids; the acrylates, such as methylmethacrylate,ethylmethacrylate, butylmethacrylate, methoxymethyl methacrylate,beta-chloroethyl methacrylate, and the corresponding esters of acrylicand alpha-chloroacrylic acids; vinyl chloride, vinyl fluoride, vinylbromide, vinylidene chloride, l-chloro-1-bromoethylene;methacrylonitrile, acrylamide and methacrylamide;alpha-chloroacrylamide, or monoalkyl substitution products thereof;methyl vinyl ketone; vinyl carboxylates, such as vinyl acetate, vinylchloroacetate, vinyl propionate, and vinyl stearate; N-

vinylimides, such as N-vinylphthalimide and N-vinylsuccinimide;methylene malonic esters; itaconic acid and itaconic ester;N-vinylcarbazole; vinyl furane; alkyl vinyl esters; vinyl sulfinic acid;ethylene alpha, beta-dicarboxylic acids or their anhydrides orderivatives, such as diethylcitraconatc, diethylmesaconate, styrene,vinyl naphthalene; vinyl-substituted teritary heterocyclic amines, suchas the vinylpyridines and alkyl-substituted vinylpyridines, for example,Z-vinylpyridine, 4-vinylpyridine, 2-methyl- S-vinylpyridine, etc.;l-vinylimidazole and alkyl-substituted l-vinylmidazoles, such as 2-, 4-,or S-methyl-lvinylimidazole, and other C=C containing polymerizablematerials.

The polymer may be a ternary interpolymer, for example, productsobtained by the interpolymerization of acrylonitrile and two or more ofany of the monomers, other than acrylonitrile, enumerated above. Morespecifically, and preferably, the ternary polymer comprisesacrylonitrile, methacrylonitrile, and Z-Vinylpyridine. The ternarypolymers preferably contain from 80 to 97 percent of acrylonitrile, from1 to percent of a vinyl pyridine or a l-vinylimidazole, and from 1 to 18percent of another substance, such as methacrylonitrile or vinylchloride.

The polymer may also be a blend of polyacrylonitrile or a binaryinterpolymer of from 80 to 99 percent acrylonitrile and from i to 20percent of at least one other C:C containing substance with from 2 to 50per cent of the weight of the blend of a copolymer of from 10 to 70percent of acrylonitrile and from to 90 percent of at least one other CC containing polymerizaole monomer. Preferably, when the polymericmaterial comprises a blend, it will be a blend of a copolymer of 90 to98 percent acrylonitrile and from 2 to 10 percent of anothermono-olefinic monomer, such as vinyl acetate, which is not receptive todyestuff, with a sufiicient amount of a copolymer of from 10 to 70percent of acrylonitrile and from 30 to 90 percent of a vinylsubstituted tertiary heterocyclic amine, such as vinylpyridine orl-vinylimidazole, to give a dyeable blend having an overallvinyl-substituted tertiary heterocyclic amine content of from 2 to 10percent, based on the weight of the blend.

The polymers, useful in the practice of the present invention, may beprepared by any conventional polymerization procedures. such as masspolymerization methods, solution polymerization methods, or acqueousemulsion procedures. However, the preferred practice utilizes suspensionpolymerization wherein the polymer is prepared in finely divided formfor immediate use in the fiber fabrication operations. The preferredsuspension polymerization may utilize bath procedures, wherein monomersare charged with an aqueous medium containing the necessary catalyst anddispersing agents. A more desirable method involves the semi-continuousprocedure in which the polymerization reactor containing the aqueousmedium is charged with the desired monomers and the continuouswithdrawal of polymer may also be employed.

The polymerization is catalyzed by means of any watersoluble peroxycompound, for example the potassium, ammonium and other water-solublesalts of peroxy acids, sodium peroxide, hydrogen peroxide, sodiumperborate, the sodium salts of other peroxy acids, and any otherwater-soluble compound containing a peroxy group (-OO-). A widevariation in the quantity of peroxy compound is possible. For example,from 0.1 to 3.0 percent by weight of the polymerizable monomer may beused. The catalyst may be charged at the outset of the reaction, or itmay be added continuously or in increments throughout the reaction forthe purpose of maintaining a more uniform concentration of catalyst inthe reaction mass. The latter method is preferred because it tends tomake the resultant polymer more uniform in its chemical and physicalproperties.

Although the uniform distribution of the reactants throughout thereaction mass can be achieved by vigorous agitation, it is generallydesirable to promote the uniform distribution of reagents by using inertwetting agents, or emulsion stabilizers. Suitable reagents for thispurpose are the water-soluble salts of fatty acids, such as sodiumoleate and potassium stearate, mixtures of water-soluble fatty acidsalts, such as common soups prepared by the saponification of animal andvegetable oils, the amino soaps," such as salts of triethanolamine anddodecylmethylamine, salts of rosin acids and mixtures thereof, thewater-soluble salts of half esters of sulfuric acid and long chainaliphatic alcohols, sulfonated hydrocarbons, such as alkyl arylsulfonates, and any other of a wide variety of wetting agents, which arein general organic compounds containing both hydrophobic and hydrophilicradicals. The quantity of emulsifying agents will depend upon theparticular agents selec ed, the ratio of monomer to be used, and theconditions of polymerization. In general, however, from 0.01 to 1.0percent by weight of the monomers may be employed.

The emulsion polymerizations are preferably conducted in glass orglassed-lined vessels which are provided with a means for agitating thecontents. Generally, rotary stirring devices are the most effectivemeans of insuring the intimate contact of the reagents, but othermethods may be successfully employed, for example by rocking or tumblingthe reactors. The polymerization equipment generally used isconventional in the art and the adaptation of a particular type ofapparatus to the reaction contemplated is within the province of oneskilled in the art. The articles manufactured therefrom may be producedby well-known conventional methods, for example, the wet-spinning,dry-spinning and melt-spinning methods for producing fibers.

The following examples are illustrative rather than limitative and allparts, proportions and percentages are by weight unless otherwisespecified.

EXAMPLE I 7.5 grams of a polymer blend of 88 percent of a copolymercontaining 94 percent of acrylonitrile and 6 percent of vinyl acetateand 12 percent of a copolymer of 50 percent of acrylonitrile and 50percent of Z-methyl-S- vinyl pyridine were added to 45 milliliters ofN,N-dimethylacetamide containing approximately 0.05 gram of titaniumdioxide. The mixture was stirred and heated to 70 C. It was then quicklycooled to room temperature and the color measured. This sample was usedas a control. The purity is set forth below. Subsequently, like sampleswere prepared but with 0.225 gram of a color inhibitor containing 0.075gram each of formaldehyde, hydroquinone and sulfuric acid; formaldehyde,p-rnethoxy phenol and sulfuric acid; and formaldehyde, phenol andsulfuric acid. The purity is set forth below.

Table l Inhibitor Percentage Purity Used Control 7.0 Formaldehyde,Hydroqulnone and Sulfuric Acid 3 6 Formaldehyde, p-Methoxy Phenol andSulfuric Acid 3 4. Formaldehyde, Phenol and Sulfuric Acid. 3 3. 9

EXAMPLE II 7.5 grams of a copolymer containing 94 percent ofacrylonitrile and 6 percent of vinyl acetate were added to 45milliliters of N,N-dimethylacetamide containing approximately 0.05 gramof titanium dioxide. The mixture was stirred and heated for 35 minutesat 70 C. It was then quickly cooled to room temperature and the colormeasured. This sample was used as a control. The purity is set forthbelow. Subsequently, like samples were prepared but with 0.225 gram ofan inhibiting agent containing 0.075 gram each of formaldehyde,hydroquinone and sulfuric acid; formaldehyde, p-methoxy phenol andsulfuric acid; and formaldehyde, phenol and sulfuric acid. The purity isset forth below.

EXAMPLE III 7.5 grams of an acrylonitrile homopolymer were added to 45milliliters of N,N-dimethylacetamide containing approximately 0.05 gramof titanium dioxide. The mixture was stirred and heated for 45 minutesat 70 C. It was then quickly cooled to room temperature and the colormeasured. This sample was used as a control. The purity of the controlsample is set forth below. Subsequently, like samples were prepared butwith 0.225 gram of an inhibiting agent containing 0.075 gram each offormaldehyde, hydroquinone and sulfuric acid; formaldehyde, p-methoxyphenol and sulfuric acid; and formaldehyde, phenol and sulfuric acid.The purity is set forth below.

Table III Inhibitor Percentage Purity Used Control 8.5 Formaldehyde,Hydroqulnone and Sulfuric Acid 3 2.4 Formaldehyde, p-Methoxy Phenol andSul- [uric Acid 3 4.4 Formaldehyde, Phenol and Sulfuric Acid.-. 3 4.

The tests for color indicative of approaching whiteness used throughoutthe examples consist of measurements of purity as calculated from thetristirnulus values determined on a General Electric spectrophotometerby the methods recommended by the Standard Observer and CoordinateSystem of the International Commission on Illumination, as fully setforth in the Handbook of Colorimetry published by The Technology Press,Massachusetts Institute of Technology in 1936.

The compositions of the instant invention present many advantages. Forexample, products formed from the polymer solutions of the instantinvention are free of objectionable color and therefore of greatercommercial value. In preparing the polymer solutions, heat may beapplied without the danger of color formation and the solutions, ifnecessary, may stand for prolonged periods and remain free of color. Theinhibiting agents are readily available and inexpensive. Therefore, nogreat increase in production cost is necessary. The compositionscontaining the inhibitors may be prepared without going through detailedand elaborate procedures that necessitate expensive changes in thedesign of the apparatus used to manufacture them.

It will be understood to those skilled in the art that many apparentlywidely different embodiments of this invention can be made withoutdeparting from the spirit and scope thereof. Accordingly, it is to beunderstood that this invention is not to be limited to the specificembodiments thereof except as defined in the appended claims.

We claim:

1. A new composition of matter comprising a polymer containing at leastpercent of polymerized acrylonitrile and up to 20 percent of anotherpolymerizable mono-olefinic monomer copolymerizable therewith, a solventtherefor, and an inhibiting agent containing substantially equalproportions by weight of formaldehyde, a compound having the generalformula,

wherein R is selected from the group consisting of hy drogen, methoxy,ethoxy and hydroxyl groups; and an inorganic acid having an ionizationconstant greater than 1X10" 2. A new composition of matter as defined inclaim 1 wherein the polymer is a copolymer containing from 80 to 98percent of acrylonitrile and from 2 to 20 percent of anotherpolymerizable mono-olefinic monomer copolymerizable therewith.

3. A new composition of matter as defined in claim 1 wherein the polymeris a blend of 80 to 99 percent of (A) a copolymer containing to 98percent of acrylonitrile and 2 to 10 percent of vinyl acetate and 1 to20 percent of (B) a copolymer containing 10 to 70 percent ofacrylonitrile and 30 to 90 percent of 2-methyl-5-vinyl pyridine.

4. A new composition of matter as defined in claim 1 wherein the polymeris polyacrylonitrile.

5. A new composition of matter as defined in claim 1 wherein theinhibiting agent contains formaldehyde, phenol and sulfuric acid.

6. A new composition of matter as defined in claim 1 wherein theinhibiting agent contains formaldehyde, p-methoxy phenol and sulfuricacid.

7. A new composition of matter as defined in claim 1 wherein theinhibiting agent contains formaldehyde, p-ethoxy phenol and sulfuricacid.

8. A new composition of matter as defined in claim 1 wherein theinhibiting agent contains formaldehyde, hydroquinone and sulfuric acid.

9. A new composition of matter as defined in claim 1 wherein the solventis N,N-dimethylacetamide.

10. A new composition of matter comprising a copolymer containing 80 to98 percent of acrylonitrile and 2 to 20 percent of vinyl acetate, asolvent therefor, and 0.3 to 15 percent, based on the total weight ofthe polymer, of an inhibiting agent, said inhibiting agent containingsubstantially equal proportions by weight of formaldehyde, a compoundhaving the general formula,

vent therefor, and 0.3 to 15 percent, based on the total weight of thepolymer, of an inhibiting agent, said in hibiting agent containingsubstantially equal proportions by weight of formaldehyde, a compoundhaving the general formula,

wherein R is selected from the group consisting of hydrogen, methoxy,ethoxy and hydroxyl groups; and sulfuric acid.

12. A new composition of matter comprising polyacrylonitrile, a solventtherefor, and 0.3 to 15 percent, based on the total weight of thepolymer, of an inhibiting agent, said inhibiting agent containingsubstantially equal proportions by weight of formaldehyde, a compoundhaving the general formula,

wherein R is selected from the group consisting of hydrogen, methoxy,ethoxy and hydroxyl groups; and sulfuric acid.

13. A method of preparing a new composition of matter comprising mixinga polymer containing at least percent of polymerized acrylonitrile andup to 20 percent of another polymerizable mono-olefinic monomercopolymerizable therewith, a solvent therefor, and an inhibiting agentcontaining substantially equal proportions by weight of formaldehyde, acompound having the general formula,

wherein R is selected from the group consisting of hy drogen, methoxy,ethoxy and hydroxyl groups; and an inorganic acid having an ionizationconstant greater than 1X 10- and heating the mixture to form ahomogeneous solution.

14. The method as defined in claim 13 wherein the polymer is a copolymercontaining from 80 to 98 percent of acrylonitrile and from 2 to 20percent of another polymerizable mono-olefinic monomer copolymerizabletherewith.

15. The method as defined in claim 13 wherein the polymer is a blend of80 to 99 percent of (A) a copolyrner containing to 98 percent ofacrylonitrile and 2 to 10 percent of vinyl acetate and 1 to 20 percentof (B) a copolymer containing 10 to 70 percent of acrylonitrile and 30to 90 percent of Z-methyl-S-vinyl pyridine.

16. The method as defined in claim 13 wherein the polymer ispolyacrylonitrile.

17. The method as defined in claim 13 wherein the inhibiting agentcontains formaldehyde, phenol and sulfuric acid.

18. The method as defined in claim 13 wherein the inhibiting agentcontains formaldehyde, p-methoxy phenol and sulfuric acid.

19. The method as defined in claim 13 wherein the inhibiting agentcontains formaldehyde, p-ethoxy phenol and sulfuric acid.

20. The method as defined in claim 13 wherein the inhibiting agentcontains formaldehyde, hydroquinone and sulfuric acid.

References Cited in the file of this patent UNITED STATES PATENTS2,502,030 Scheiderbauer Mar. 28, 1950 2,688,008 Chaney et al. Aug. 31,1954 2,730,436 Young et al. Ian. 10, 1956

1. A NEW COMPOSITION OF MATTER COMPRISING A POLYMER CONTAINING AT LEAST80 PERCENT OF POLMERIZED ACRYLONITRILE AND UP TO 20 PERCENT OF ANOTHERPOLYMERIZABLE MONO-OLEFINIC MONOMER COPOLYMERIZABLE THEREWITH, A SOLVENTTHEREFOR, AND AN INHIBITING AGENT CONTAINING SUBSTANTIALLY EQUALPROPORTIONS BY WEIGHT OF FORMALDEHYDE, A COMPOUND HAVING THE GENERALFORMULA,